Natural gas hydrates occupying fractures: A focus on non-vent sites on the Indian continental margin and the northern Gulf of Mexico

We present a review of the geophysical and petrophysical properties of gas hydrate-filled fracture sites that are not associated with a gas vent or chimney from the Indian National Gas Hydrate Program Expedition 01 and the Gulf of Mexico Gas Hydrate Joint Industry Project Legs I & II. We analyzed logging-while drilling (LWD) resistivity images, well logs and coring information at eight of these sites and found in all cases that the gas hydrate-filled fractures occurred in fine-grained sediments, were near-vertical, and were generally oriented in the same direction at each site. In addition, resistivity was the only physical property always affected by presence of near-vertical gas hydrate-filled fractures, though in one case only the LWD resistivity image detected the presence of gas hydrate. Gas hydrate-filled fractures did not intersect the base of the gas hydrate stability zone at the location of the wellbore at any of the sites. We suggest that at non-vent/non-chimney sites the methane occupying the gas hydrate is likely produced microbially in situ and is not sourced from below.